Functional morphology and hydrodynamics of plesiosaur necks: Does size matter?

Plesiosaurs are an enigmatic, diverse extinct group of Mesozoic marine reptiles well-known for their unique body plan with two pairs of flippers and usually an elongated neck. The long neck evolved several times within the clade, yet the evolutionary advantages are not well understood. Previous studies have mainly focused on swimming speeds or flipper locomotion. We evaluated the hydrodynamics of neck length and thickness in plesiosaurs using computational fluid dynamics (CFD) simulations based on the Reynolds-Averaged Navier-Stokes (RANS) approach. Simulations were performed of flow patterns forming around five distinctive plesiosaur models, three of different neck lengths (neck/body ratios of 0.2, 0.41, and 0.63) and two of different neck thicknesses (100% and 343% increase compared to cervical vertebrae width). By simulating water flow past the three-dimensional digital plesiosaur models, our results demonstrated that neck elongation does not noticeably affect the force of drag experienced by forward swimming plesiosaurs. Thicker necks did reduce drag compared with thinner necks, however. The consistent drag coefficient experienced by the three neck lengths used in this study indicates that, at least for forward motion at speeds from 1-10m/s, hydrodynamic implications were not a limiting selective pressure on the evolution of long necks in plesiosaurs. We also tested the effects of bending the long neck during forward motion. Bending a plesiosaur neck evenly in lateral flexion increased the surface area normal to flow, and subsequently increased drag force. This effect was most noticeable in the longest necked forms

An exact collisionless equilibrium for the force-free Harris sheet with low plasma beta

We present a first discussion and analysis of the physical properties of a new exact collisionless equilibrium for a one-dimensional nonlinear force-free magnetic field, namely, the force-free Harris sheet. The solution allows any value of the plasma beta, and crucially below unity, which previous nonlinear force-free collisionless equilibria could not. The distribution function involves infinite series of Hermite polynomials in the canonical momenta, of which the important mathematical properties of convergence and non-negativity have recently been proven. Plots of the distribution function are presented for the plasma beta modestly below unity, and we compare the shape of the distribution function in two of the velocity directions to a Maxwellian distribution

Evidence-based decision support for pediatric rheumatology reduces diagnostic errors.

BACKGROUND: The number of trained specialists world-wide is insufficient to serve all children with pediatric rheumatologic disorders, even in the countries with robust medical resources. We evaluated the potential of diagnostic decision support software (DDSS) to alleviate this shortage by assessing the ability of such software to improve the diagnostic accuracy of non-specialists. METHODS: Using vignettes of actual clinical cases, clinician testers generated a differential diagnosis before and after using diagnostic decision support software. The evaluation used the SimulConsult® DDSS tool, based on Bayesian pattern matching with temporal onset of each finding in each disease. The tool covered 5405 diseases (averaging 22 findings per disease). Rheumatology content in the database was developed using both primary references and textbooks. The frequency, timing, age of onset and age of disappearance of findings, as well as their incidence, treatability, and heritability were taken into account in order to guide diagnostic decision making. These capabilities allowed key information such as pertinent negatives and evolution over time to be used in the computations. Efficacy was measured by comparing whether the correct condition was included in the differential diagnosis generated by clinicians before using the software ( unaided ), versus after use of the DDSS ( aided ). RESULTS: The 26 clinicians demonstrated a significant reduction in diagnostic errors following introduction of the software, from 28% errors while unaided to 15% using decision support (p \u3c 0.0001). Improvement was greatest for emergency medicine physicians (p = 0.013) and clinicians in practice for less than 10 years (p = 0.012). This error reduction occurred despite the fact that testers employed an open book approach to generate their initial lists of potential diagnoses, spending an average of 8.6 min using printed and electronic sources of medical information before using the diagnostic software. CONCLUSIONS: These findings suggest that decision support can reduce diagnostic errors and improve use of relevant information by generalists. Such assistance could potentially help relieve the shortage of experts in pediatric rheumatology and similarly underserved specialties by improving generalists\u27 ability to evaluate and diagnose patients presenting with musculoskeletal complaints. TRIAL REGISTRATION: ClinicalTrials.gov ID: NCT02205086

Patient preferences for topical treatment of actinic keratoses:a discrete-choice experiment

Funding: This study was funded by the National Institute for Health Research (NIHR) Research for Patient Benefit programme (PB-PG-0110-21244), Department of Health, UK. The funder was not involved in the study design. Acknowledgments: The authors gratefully acknowledge support from the Cancer Research UK Clinical Trials Unit, the UK Dermatology Clinical Trials Network, the NIHR Clinical Studies Group, and support for investigators from the British Skin Foundation and Cancer Research UK. We would also like to thank Martin Jones, Daniel Rigby and Ariel Bergmann for constructive comments on the design of the DCE.Peer reviewedPostprin

The development of a space climatology: 3. Models of the evolution of distributions of space weather variables with timescale

We study how the probability distribution functions of power input to the magnetosphere Pα and of the geomagnetic ap and Dst indices vary with averaging timescale, , between 3 hours and 1 year. From this we develop and present algorithms to empirically model the distributions for a given and a given annual mean value. We show that lognormal distributions work well for ap, but because of the spread of Dst for low activity conditions, the optimum formulation for Dst leads to distributions better described by something like the Weibull formulation. Annual means can be estimated using telescope observations of sunspots and modelling, and so this allows the distributions to be estimated at any given between 3 hour and 1 year for any of the past 400 years, which is another important step towards a useful space weather climatology. The algorithms apply to the core of the distributions and can be used to predict the occurrence rate of “large” events (in the top 5% of activity levels): they may contain some, albeit limited, information relevant to characterizing the much rarer “superstorm” events with extreme value statistics. The algorithm for the Dst index is the more complex one because, unlike ap, Dst can take on either sign and future improvements to it are suggested

Particle-in-cell experiments examine electron diffusion by whistler-mode waves: 2. Quasilinear and nonlinear dynamics

Test-particle codes indicate that electron dynamics due to interactions with low amplitude incoherent whistler mode-waves can be adequately described by quasilinear theory. However there is significant evidence indicating that higher amplitude waves cause electron dynamics not adequately described using quasilinear theory. Using the method that was introduced in Allanson et al. (2019, https://dx.doi.org/10.1029/2019JA027088), we track the dynamical response of electrons due to interactions with incoherent whistler-mode waves, across all energy and pitch angle space. We conduct 5 experiments each with different values of the electromagnetic wave amplitude. We find that the electron dynamics agree well with the quasilinear theory diffusion coefficients for low amplitude incoherent waves with $(B_{\text{w,rms}}/B_0)^2\approx 3.7\cdot 10^{-10}$, over a timescale $T$ of the order of 1000 gyroperiods. However the resonant interactions with higher amplitude waves cause significant non-diffusive dynamics as well as diffusive dynamics. When electron dynamics are extracted and analyzed over timescales shorter than $T$, we are able to isolate both the diffusive and non-diffusive (advective) dynamics. Interestingly, when considered over these appropriately shorter timescales (of the order of hundreds or tens of gyroperiods), the diffusive component of the dynamics agrees well with the predictions of quasilinear theory, even for wave amplitudes up to $(B_{\text{w,rms}}/B_0)^2\approx 5.8\cdot 10^{-6}$. Quasilinear theory is based on fundamentally diffusive dynamics, but the evidence presented herein also indicates the existence of a distinct advective component. Therefore, the proper description of electron dynamics in response to wave-particle interactions with higher amplitude whistler-mode waves may require Fokker-Planck equations that incorporate diffusive and advective terms